Laminaria is a seaweed that has been grown in China, Japan, and Korea for many centuries. It is used as a high energy food in Northern China in the wintertime when food is scarce. It is composed of essential electrolytes, vitamins, and minerals. It was found that when Laminaria is dried, shaped in the form of a small pen, and sterilized, it can be used to cause priming of the cervix (softening and dilation) to occur. It is used in first trimester, second trimester and late term abortions to reduce the incidence of cervical tears, uterine perforation (hole in uterine wall), retained pregnancy tissue or excessive uterine bleeding. This decreases the chance of infection, hospitalizations, bowel injury, hysterectomy, blood transfusions, and maternal death.

One or several Laminaria placed in the cervix of patients in the first or second trimester of pregnancy and retained for three to four hours, is generally enough time to allow for adequate opening and softening of the cervix to occur in patients up to 16 weeks gestation. This allows safe removal of the pregnancy tissue. In patients 16 weeks or further, the Laminaria may need to remain in the cervix over night to allow for further dilation (opening) of the cervix to occur and the tissue can be removed the next day. It is not uncommon for it to take a second day of removal of the original Laminaria, replace them with more Laminaria and not remove the fetal tissue until the third day. This allows more softening and dilatation of the cervix to take place.

Second day insertion of Laminaria has become less common since combining with Misoprostol which allows most pregnancy tissue to be removed on the second day of the abortion procedure.

Laminaria are generally safe. Complications are rare but include infection, breaking off inside the uterus, perforation of the uterus, and an allergic reaction where patients may experience mild generalized itching to a total anaphylactic (hives, itching, lowering of blood pressure, leakage of capillaries leading to edema (and rarely death. The most common side effect of Laminaria is lower abdominal cramping which is due to the opening and softening of the cervix.